1. Field of the Invention
The present invention relates to an A/D conversion process.
2. Description of Prior Art
There has recently been developed a highly integrated circuit in which at least an A/D converter and an input-output buffer are built in a single chip.
Such a highly integrated circuit has a disadvantage that an ON/OFF inversion in an output port controlling a large current sometimes affects a value converted by the A/D converter to cause an error in the converted value. More specifically, in a highly integrated circuit used in an engine control unit controlling the engine, if an A/D converter has a dynamic range from 0 to 5 V and outputs a 10-bit digital signal in response to an inputted analog signal, the A/D converter carries out an A/D conversion with a resolution of approximately 5 mV. An output buffer is, on the other hand, connected with a base terminal of a transistor which serves to drive an injector to control an electric current of a several amperes, therefore being drivable by a current of 50 to 100 mA as a base current. In consequence, an inversion, for example a change in an ON/OFF state in an output port of the output buffer, may affect a value converted by the A/D converter, leading to an error in the converted value.